Mutations in mitochondrial DNA (mtDNA) are inherited exclusively from our mothers and can cause a broad range of debilitating and fatal diseases. Reproductive technologies designed to uncouple the inheritance of the mitochondrial genome from the nuclear DNA genome may enable affected women to have a genetically related child with a greatly reduced risk of mtDNA disease. Such technologies involve transplantation of the nuclear DNA from the egg of an affected woman to an enucleated egg from an unaffected donor. Nuclear genome transplantation can be performed either before or after fertilisation. The latter involves transfer of pronuclei, which separately contain the maternal and paternal genomes. In parallel with legal and regulatory reform to permit therapeutic application of so called “mitochondrial donation” techniques in the UK, we have conducted preclinical studies to test the safety and efficacy of pronuclear transplantation (PNT). Taking account of our findings the Human Fertilisation and Embryology Authority (HFEA) have approved the cautious use of PNT in the UK and our clinic has been granted the first licence for its therapeutic application. Our ongoing research aims to further refine and develop nuclear genome transplantation techniques to break the cycle of disease transmission from mother to child.